Currently, for the connection between a display panel in a liquid crystal display device or other active matrix-type display device and a driving circuit for driving the display panel, adopted are the TCP (Tape Carrier Package) system or the COG (Chip on Glass) system, the monolithic system utilizing low temperature polycrystalline silicone techniques, and the like.
In the TCP system, as illustrated in FIG. 11, with respect to a display panel 101, a plurality of gate TCPs 103, each having mounted thereon a gate IC (Integrated Circuit) 102 serving as a gate signal line driving circuit, and a plurality of source TCPs 105 each having mounted thereon a source IC 104 serving as a source signal line driving circuit are connected. Further, these gate TCPs 103 and source TCPs 105 are respectively connected to a gate PWB (Printed Wire Bonding) 106 and a source PWB 107 for inputting signals to these TCPs. Each of these PWBs is connected to an external circuit substrate via an FPC (Flexible Printed Circuit) 108.
In the COG system, as illustrated in FIG. 12, on a liquid crystal panel 111, a plurality of gate ICs 112 serving as a gate source line driving circuit and a plurality of source ICs 113 serving as a source signal line driving circuit are mounted. These gate ICs 112 and source ICs 113 are connected to a gate FPC 114 and a source FPC 115 respectively for inputting signals to be connected to an external circuit substrate via these gate FPC 114 and source FPC 115.
The foregoing TCP system and the COG system are advantageous in long-term good record for mass-production, quality and reliability, whereas disadvantageous in that high costs are required for raw materials and mounting.
In the monolithic system, the gate IC and the source IC adopted in the foregoing COG system are integrated in the display panel utilizing the low temperature polycrystalline silicone techniques. This system permits a reduction in the number of required components as compared to the cases of adopting the TCP system or the COG system, which results in cost reduction for raw materials and mounting. In this way, however, the design on the side of the display panel becomes complicated, which, in turn, increases costs. Furthermore, the monolithic system is certainly disadvantages for a large-size display panel, and thus the applicable range for the monolithic system is limited.
Other than the foregoing three systems, for example, Japanese Unexamined Patent Application No. 04-283727/1992 (Tokukaihei 04-283727, published on Oct. 8, 1992) discloses the GOG (Glass on Glass) system utilizing the same amorphous silicone for the display panel, as adopted in the TCP system or the COG system, at the same costs for raw materials or lower than the monolithic system. In the GOG system, as illustrated in FIG. 13, signals are input from a FPC 124 into a gate GS (Glass Stick) 122 and a source GS 123 having mounted thereon ICs serving as a driving circuit via on a display panel 121, thereby driving the display panel 121.
In the GOG system, the section for the driving circuit which can be a cause for a lower quality in the monolithic system is prepared in separate steps as the gate GS 122 and the source GS 123. Therefore, in the GOG system, a cost increase due to lower yield of the display panels 121 can be suppressed, and the required number of components can be reduced as compared to the TCP system or the COG system.
However, in the conventional structure, particularly in the TCP system and the GOG system, a connection inferior is liable to occur between the substrate having mounted thereon the display panel (hereinafter referred to as a display panel side substrate) and the substrate having mounted thereon an IC serving as a driving circuit (hereinafter referred to as a driving circuit side substrate), due to, for example, foreign substances being contaminated into the connected part, which would cause an opening or leakage. Furthermore, in order to correct such connection inferior, the following problems arise.
In the TCP system, in order to correct the connection inferior, first, a part of the TCP, subjected to the connection inferior between the display panel side substrate and the driving circuit side substrate, is separated. Then, after cleaning residual resin for connection remaining on the surface of the panel, a new TCP or IC is connected again. However, this correction method requires quite a few steps, and an operating efficiency would be lowered.
Furthermore, when adopting the foregoing correction method in the GOG system, as adopted in the TCP system, to fix the opening or leakage resulting from connection inferior between the substrates such as contaminations of foreign substances, other than the problem of insufficient operation efficiency, the following problem arises. Namely, although the GOG system is advantageous over other system in costs, the GOG system presents a serious problem in that an increase in percentage defective in the GOG connection resulting from contamination of foreign substances or difficulties in GS exchange in the case of generating connection inferior would be a serious problem.
Firstly, the problem of an increase in percentage defective, resulting from foreign substances contaminated in the substrate connected part in the GOG system will be explained in reference to FIGS. 14(a) through 15(b). FIG. 14(a) is a sectional view taken along an arrow A–A′ of FIG. 11, and shows the state where foreign substances are contaminated between substrates to be connected. FIG. 15(a) is a sectional view taken along an arrow B–B′ of FIG. 13, and shows the state where foreign substances are contaminated between substrates to be connected.
As illustrated in FIG. 14(a), for the TCP system, a terminal 109 on the part of the display panel side substrate subjected to the contamination of foreign substances 131 is separated from a terminal 110 on the driving circuit side substrate. However, as the TCP side substrate has certain flexibility, the connection between terminals adjacent to the foreign substances 131 as contaminated can be ensured. Furthermore, as illustrated in FIG. 14(b), in the case where the terminals to be connected have relatively long connection area, irrespectively of the foreign substances 131, the connection between terminals subjected to the contamination of the foreign substances 131 can be ensured in an area separated from the foreign substances 131.
In contrast, in the GOG system, as illustrated in FIG. 15(a), the substrate does not have flexibility, not only a terminal 125 of the display panel side substrate 1 and a terminal 126 on the driving circuit side substrate, which are subjected to the contamination of the foreign substance 131, but also a terminal adjacent to the terminal 125 and a terminal adjacent to the terminal 126 are liable to be open. Furthermore, as illustrated in FIG. 15(b), even in the case where the terminals to be connected have relatively long connection area, the connection between the terminals cannot be ensured even in an area apart from the foreign substance 131.
Furthermore, in the GOG system, the wiring on the GS glass for the driving circuit side substrate is formed in a thin film in thickness of not more than 1 μm. Therefore, electrically conductive particles (ø 5 to 10 μm) in an anisotropic conductive film serving as a connection material between the substrates are agglomerated not only at the terminals but also in a space between the terminals, and thus a leakage due to the connection between the electrically conductive particles is liable to occur. In contrast, in the TCP system, the wiring on the TCP has a thickness in a range of around from 10 to 30 μm, which is sufficiently larger with respect to the wiring thickness formed by a thin film on the GS glass. Thus, particles are less liable to be agglomerated between terminals.
Next, the problem associated with the difficulty in exchanging the driving circuit in the case of generating the connection inferior in the wiring in the connected part between the substrates will be explained. When the GOG system is applied to a device of a large size, the driving circuit side substrate becomes larger in size (for example, in the case of applying the GOG system to a 15″ class module, the long side of the substrate becomes around 300 mm). Thus, such problem as the driving circuit side substrate or the display panel side substrate being cracked is liable to occur in separating the driving side substrate.
Even if there is only one connection inferior, the whole driving circuit side substrate needs to be replaced unlike the TCP system whereby each TCP is replaceable.
Incidentally, other than the foregoing correction method of a connection inferior resulting from the contamination of foreign substances, a correction method of disconnecting by applying a laser beam with respect to the foreign substances may be adopted. However, the electrically conductive foreign substances generally have a thickness of around several tens μm s, and thus it is technically difficult to separate only the foregoing substances through the glass substrate without causing any damage to the electrode terminal.
As described, in the conventional method, particularly in the GOG system, an increase in the connection inferior generation ratio, the difficulty in correcting the connection inferior, or the resulting damage of a display panel from the correction error, an increase in the number of operations, a cost increase for the materials required for the necessary correction, generation of secondary inferior which possibly occur when correcting, lower quality would be the problem.